1. Field of the Invention
The present invention relates to a smelting reduction of Ni ore, and more particularly to a method for smelting reduction of Ni ore wherein a converter type smelting reduction furnace is used and a slopping due to slag produced in large quantities is prevented from taking place.
2. Description of the Prior Arts
Stainless steel has previously been manufactured by melting scrap and ferrochrome and ferronickel being ferro alloy or electrolytic nickel in an electric furnace. That is, Cr and Ni being the main components of stainless steel has been obtained by melting ferro alloy having previously been reduced in an electric furnace. Against such prior art method, recently, attention is paid in terms of energy saving and a decrease of a manufacturing cost to a smelting reduction method wherein molten metal with high chromium content is obtained directly from Cr ore as a chromium source.
As far as Cr was concerned, it is tried to manufacture stainless steel by directly reducing Cr ore in a converter type smelting reduction furnace as described above. However, it has not been tried to manufacture stainless steel by directly reducing Ni ore. The reason for this is that, since only about 2 to 3% Ni is contained in Ni ore, a great amount of Ni ore has to be used for manufacturing stainless steel by directly reducing Ni ore; operations of the converter type furnace are thus regarded as difficult. In the case of manufacturing stainless steel of 8% Ni, for example, 3 to 4 tons of Ni ore per ton of stainless steel are used. Accordingly, during a smelting reduction of Ni ore, there is a possibility of a break of operations, damage of equipment or a decrease of the yield of Ni due to occurrence of the slopping in connection with production of a great amount of slag. On the other hand, when the slag is many times discharged from a furnace to avoid the occurrence of the slopping, there is a possibility such that the yield of Ni decreases extremely as a result of an escape of molten metal during discharge of the slag and an efficiency in work decreases.